PROJECT ABSTRACT Epigenetics impacts all areas of cellular physiology, and epigenetic dysregulation is pervasive in human disease. Given the inherent reversibility of epigenetic changes, this presents a great opportunity for the discovery of novel therapeutics given the recent rapid development of epigenome-modifying drugs. Intriguingly, large-scale human sequencing efforts have revealed that sun-damaged, but clinically otherwise normal human skin, can harbor frequent mutations in epigenetic chromatin modifying enzymes. These include mutations that have been typically observed in cutaneous squamous cell carcinoma (cSCC), the second most common of all human malignancies, and a major economic and public health burden. Recent data suggests that these epigenetic mutations may be important drivers of malignant clone formation in the epidermis, provoking the hypothesis that proper epigenetic function is required for both maintaining epidermal homeostasis and preventing the initiation of carcinogenesis. Remarkably, despite the high incidence of both these mutations in epigenetic modifiers and cSCC, the precise mechanisms by which disruption of chromatin modifying enzymes drives the initiation of cSCC are virtually unknown. In this proposal, we will utilize multiple model systems including human patient samples and a variety of transgenic mouse models, combined with several innovative genome-wide and functional technologies in order to define the mechanistic links between chromatin regulation, transcription, epidermal cell fate, and the initiation of epidermal carcinogenesis. Collectively, these studies promise to inform both the development and utilization of epigenetic therapies in the future.